In a Wavelength Division Mutiplexing (WDM) optical network, the put forwarding of Path Compute Element (PCE) and Path Compute Element Communication Protocol (PCEP) provides a practicable approach for a spanning path computation, and meanwhile creates a condition for interconnection and intercommunication of TE LSP computations of products of different manufacturers. Wherein, the WDM optical network includes multiple regions, each region includes multiple nodes, and the PCE in each region is configured with Traffic-Engineering Database (TED) of the current region and is responsible for path computing of the nodes in the current region. Since the TED of different regions is not shared, the PCE in a certain region only knows the Traffic-Engineering Database (TED) of the current region. If two nodes in different regions need to communicate, since the PCE of each region can not acquire the TED of other regions, the TE LSP can not be established for the two nodes, thus PCEs in different regions are required to perform the spanning path computation collaboratively. The related art gives a method for the spanning path computation: Backward-Recursive PCE-Based Computation (BRPC). The BRPC is a method for collaboratively collecting paths between the PCEs, but when the BRPC is used, the PCE of a region in which a source node is located needs to acquire a precondition for implementing the BRPC, which includes:
each PCE knowing a PCE corresponding to its adjacent region;
a region in which a target node is located;
a region passed by the TE LSP of the source node and target node;
boundary nodes in the region passed by the TE LSP of the source node and target node;
ingress boundary nodes and egress boundary nodes in the region passed by the TE LSP of the source node and target node.
In the related art, however, a method for how to acquire the above precondition is not given, which cause that the BRPC can not be used to perform the spanning path computation.